Han Yuan’s article “Palladium(II) Pyrazolin-4-ylidenes: Remote N-Heterocyclic Carbene Complexes and Their Catalytic Application in Aqueous Suzuki-Miyaura Coupling“, published in Organometallics is being featured on the ACS Publications website as a Most-Accessed Article for the fourth-quarter (Oct-Dec) of 2007. 🙂
7 thoughts on “Most-Accessed article :)”
Well Done! You are the best carbene chemist in Singapore. Beware of copycats!
Copycats can never be avoided. You just have to do better than them. If this “copycat” happens to be a big dog, at least you could share some prizes with him/her if this type of work receives high appreciation. BTW, there is another nice asap in OM today.
Saw the paper. Wonder if there are really agostic interactions between the H atoms and the metal. Well, 4 of the 5 d-orbtials of Pd are filled with electrons and the only one which is empty is lying on the x-y plane, so which metal orbitals are forming the agostic interactions with the H atoms?
Or could it be H-bonding?
Or using Ockham’s razor, it is rather pointless to ascribe any bonding.
Ubersteppenwolf
Hello Ubersteppenwolf,
which paper do you refer to? The current asap paper has no Pd! In any case, you must read the paper carefully, since I have spent a lot of time writing it 😉
To reply to some of your comments:
1. I have never published ANY paper about agostic interactions.
2. These anagostic/preagostic (NOT agostic) interactions are weak and cannot be really described as a true bond. Too bad, I also haven’t discovered them first. Venanzi and Pregosin, Bergman and Ellman, Crabtree and Eisenstein among others have described them as well, however in non-NHC systems.
3. According to some references indicated in my papers, these anagostic/preagostic interactions result from “donation” of filled dz2 or dxz/yz orbitals into the antibonding C-H orbital. The “true” nature is still under debate, but isn’t this what science is about?
4. And yes they are more similar to H-bonding than to agostic interactions. Both lead to a significant downfield shift of the corresponding proton, whereas an agostic proton experiences a highfield shift.
Prost, der Herr.
Entschuldigung. I was not careful when I wrote my last comment. You know, there are many copycats working on palladium NHC complexes. Just wonder the distance between Ni and H are shorter than the sum of their covalent radii? It would be good if the alkyl group is CH3 because it will remove the doubt that the orientaion of the proton is not due to steric effect.
How about the absorption spectrum of the complex. Just wonder the position of the ligand field transition. It may give some idea about the position of the carbene in spectrochemical series. Well, it could be done by some other people.
Servus!
Ubersteppenwolf
Moin moin Uebersteppenwolf,
yes, the C-H-Ni distance is shorter than the sum of their van der Waals radii, but I don’t think that you can convince people with this argument. We have synthesized Me-analogues as well, but these do not exhibit such preagostic or anagostic interactions. The free rotation leads to an average signal for the 3 protons and no significant downfield shift can be observed. For our system isopropyl or benzhydryl are the best substituents to place a single proton above the metal center. And yes, steric effects are important. The proton must be held in that orientation to experience these weak interactions.
We have also done some absorption spectra on these type of complexes, however only transitions due to the aromatic backbone can be observed. We will try to look into that in more detail. Thanks for the suggestion.
Und Tschuess…
vielen dank!
I am not familar with the inorganic chemists in your country but apparently you are doing some very good stuff. I heard there is another good organometallic chemist in your country called Leong something. I bet you young people will put Singapore on the World map of organometallics. Looking forward to new papers from you guys.
Servus
Uebersteppenwolf